Trecolori is an excellent suggestion. It's one of our favorites in that part of town. For 20 people, they offer a sit-down dinner in their private room for $25, $35 or $40pp. You can see details here: http://www.trattoriatrecolori.com/eve...

I've never been to Dell'Arte, so I can't compare them. What I do know is it's famous for the antipasti bar and the unusual decor, i.e., plaster body parts! Perhaps, other Hounds will chime in and tell you how good the food is.